In apparatus such as waste handling or resource recovery systems it is well known that a drum which is rotatable about its longitudinal axis may be used to separate materials into light and heavy fractions. This is done by tilting the drum's axis to a selected angle and depositing materials of mixed weights in the interior of the drum as it is being rotated. Simultaneously therewith a stream of air at relatively high velocity is made to flow upwardly through the drum. Heavy materials will proceed to make their way downwardly and out the lower end of the drum while light materials will be entrained in the air stream and carried out the upper end of the drum.
Such apparatus is fully shown and described in U.S. patent application Ser. No. 580,372, filed May 22, 1975, and owned by the assignee of the present invention.
In such apparatus the light materials which are carried out the upper end of the drum enter a plenum or other collector. To achieve this the upper end of the drum is inserted into the plenum through an opening in a side wall thereof. However, the drum cannot be attached to the plenum wall in a tight fit because it must be permitted to rotate and to be angled as desired.
This, then, poses severe problems since it is also necessary to prevent any substantial amounts of air from passing between the drum and plenum wall. To provide the air stream within the drum for entrainment of light fractions, a fan or blower is mounted in a position to draw air upwardly through the drum and sequentially through the plenum. It will be apparent that if an air seal of some sort is not provided between the rotary drum and plenum wall, air will be drawn through this space and will considerably affect the flow of air through the drum. This could render the system unworkable or could require the use of an oversized fan system.